The availability of liquid biopsies, such as sampling of blood to measure key disease biomarkers, could aid in the detection of blood-circulating tumor DNA (ctDNA) known to confer resistance to cancer therapy. For example, the T790M mutation in the epidermal growth factor (EGFR) accounts for 50% of acquired resistance to FDA-approved EGFR targeted therapies. Detection of this mutation is important to evaluate disease relapse and guide the selection of alternative therapies for better treatment outcome. Therefore, identification of ctDNAs that harbor EGFR-specific drug resistant mutations needs to be noninvasive. However, detection of ctDNAs is challenging because they constitute a small fraction of the total number of normal circulating DNA in blood. Current detection methods rely on digital PCR-based techniques, which are limited because of high cost, need for highly trained operators, requirement for time-consuming sample purification steps, slow sample-to-answer time, and limited ability for parallel analysis of a large number of biomarkers. To address this need, Giner, Inc. proposes to develop an electrochemical biosensor for multiplexed detection of ctDNA biomarkers associated with acquired resistance to EGFR-targeted therapies. This sensor will be designed to achieve both selective and sensitive detection of ctDNA in human serum at physiological relevant concentrations.